Valve packing assembly

ABSTRACT

A turbine fuel valve packing assembly including two sets of packing rings in which at least one packing ring is a V-shaped packing ring, a compression member, lantern ring, and packing gland with a sealing ring is disclosed which effectively seals turbine fuel valves against leaking. Further disclosed is a valve packing replacement method utilizing a bifurcated valve shaft allowing part of the shaft to be removed, thereby providing enough space for the valve packing assembly to be removed from the fuel valve and replaced without disassembling the entire fuel valve.

This is a division of application Ser. No. 08/568,261 filed Dec. 6,1995, now U.S. Pat. No. 5,657,785.

BACKGROUND OF THE INVENTION

This invention relates to valves, valve packing, and methods of valvepacking replacement for turbines.

Gas turbines utilize a plurality of valves to control the amount of fuelbeing burned by the turbine. These valves must be packed to seal againstfuel leaks. Because of the environmental regulations presentlyapplicable to these valves, any leak through the packing of the valvemust be repaired.

A typical valve comprises a valve shaft which extends through a stuffingbox which houses the packing for the valve. One end of the valve shaftis external to the valve and is operated on by an actuator while theother end of the valve shaft is internal to the valve and operates toopen and close the valve. The packing for the valve typically includes acompression member, usually a coiled spring with an aperturetherethrough large enough to receive the valve shaft. The spring isplaced in the stuffing box toward the internal end of the valve shaft.Thus, the valve shaft extends through the aperture of the compressionmember, and the compression member is inserted into the stuffing boxtoward the valve end of the valve shaft. Following the spring, threeTEFLON® packing rings are placed over the valve shaft and pushed up intothe stuffing box. Next, a conventional lantern ring with a centralaperture is placed over the valve shaft and inserted up into thestuffing box. Finally, a packing gland having a centrally locatedaperture is placed over the valve shaft. The packing gland has a flangeextending radially outward from the valve shaft for attachment to thevalve and a flange extending axially into the stuffing box, so that whenthe packing gland is attached to the valve case, the spring iscompressed thereby compressing the packing rings and expanding thepacking rings radially outward and radially inward to create a sealbetween the valve shaft and the stuffing box wall. This packing assemblyallows the valve shaft to translate longitudinally through the stuffingbox and is designed to prevent fuel leaks. A sealing ring is providedbetween the lantern ring and the packing gland to prevent externalcontaminants from being introduced into the stuffing box and damagingthe packing.

The turbine fuel valves operate at temperatures around 300° F. andpressures ranging from 120 psig. to 330 psig. Under these conditions thevalve packing described has failed frequently creating environmentalcompliance problems.

Because the cabinet in which the valves are housed does not provideenough space for the valve shaft to be pulled far enough out of thevalve to remove the valve packing assembly from the stuffing box, it isnecessary to dismantle the valve to repair the valve packing. Thus, thevalve must be bypassed and completely disassembled to remove the packingrings and the sealing ring. Because the valves must be bypassed andcompletely dismantled, the repair takes approximately 12-16 hours.Further, because the sealing ring is interposed directly between thepacking gland and lantern ring, it is in direct contact with thestuffing box wall, and thus, it must be scraped off the stuffing boxwall before the new packing is placed into the stuffing box. Againbecause the cabinet in which the valves are housed provides limited workspace, this is a time consuming and difficult task. Therefore, valvepacking assembly repair is time consuming and costly.

The time required to complete valve packing changes increases the costof running the turbine. Further, the frequency with which the valvepacking is repaired adds to the cost of running the turbine. It isdesirable, therefore, to reduce the amount of time necessary to repairthe valve packing and to reduce the frequency with which the valvepacking fails.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a novel valvepacking assembly located in a stuffing box of a turbine fuel valve. Thevalve packing assembly seals the valve from atmosphere and comprises acompression member, a first set of packing rings, a lantern ring, and asecond set of packing rings.

In a preferred embodiment of the valve packing assembly, a packing glandis used to hold the lantern ring and the two sets of packing ringsinside the stuffing box. The packing gland also defines a counterborewhich holds a sealing ring against the valve shaft to seal the stuffingbox from external contaminants. Each set of packing rings comprisesthree packing rings that are V-shaped. The packing rings are fabricatedfrom TEFLON® impregnated with graphite.

The preferred embodiment of the assembly further includes a crossheaddefining a shaft receiving area with a stub shaft receiving side and avalve shaft receiving side. A valve shaft is inserted into the valveshaft receiving side of the shaft receiving area and a stub shaft isinserted into the stub shaft receiving side of the shaft receiving area,so that the two shafts abut each other. The shaft receiving area isdefined between two legs of the crosshead and are held between the twolegs of the crosshead with pins. The shafts are further held securely inthe crosshead by a tightening mechanism which pinches the two shaftsbetween the legs of the crosshead.

There is further provided in the present invention a valve packingmethod and valve packing replacement method to replace packing locatedin a stuffing box for sealing a fuel valve of a turbine comprisingplacing a compression member over the valve shaft and into the stuffingbox, placing a first set of packing rings into the stuffing box followedby a lantern ring, and placing a second set of packing rings into thestuffing box. After the second set of packing rings is inserted into thestuffing box, a packing gland is placed over the valve shaft andattached to the valve to compress the first and second sets of packingwith the compression member. Thus, the packing rings expand outwardlyand inwardly to seal the valve. To change the packing, the stub shaft isdisconnected and removed from the crosshead and the valve shaft is slidin a direction out of the valve to remove the packing assembly from thestuffing box. The valve packing assembly is removed from the shaft andreplaced. The crosshead is then reattached to the valve shaft and thestub shaft reattached to the crosshead. The sealing ring may also bechanged during this process. In a preferred embodiment of the method, atleast one of the packing rings has a V-shape and is fabricated fromgraphite impregnated TEFLON®.

These and other features and advantages of the present invention willappear from the following Detailed Description and the accompanyingdrawings in which similar reference characters denote similar elementsthroughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a turbine fuel valve and a cabinet housingthe valve;

FIG. 2 is an exploded perspective view, inverted for clarity, of thevalve packing assembly and shafts according to the present invention;

FIG. 3 is a perspective view of a generally V-shaped ring;

FIG. 4 is a cross-sectional view of a generally V-shaped ring takenalong line 4--4 of FIG. 3;

FIG. 5 is a top view of a packing gland used in the valve packingassembly which includes a sealing ring; and

FIG. 6 is a cross-sectional view of the packing gland and sealing ringof FIG. 5 taken along line 6--6 of FIG. 5.

DETAILED DESCRIPTION

FIG. 1 schematically shows a steam turbine fuel valve, generallydesignated 10, contained in a valve cabinet 12. The valve comprises aninlet opening 14 and outlet opening (not shown). To open and close theinlet opening, a valve shaft 16 extends in one direction through acylindrical stuffing box 18 and through the valve to the inlet opening.The valve shaft extends in the other direction out of the valve to anactuator (not shown) The actuator translates the valve shaftlongitudinally to open and close the inlet opening. The valve shaft isallowed to translate longitudinally through the contents (i.e. thepacking assembly) of the stuffing box which act to seal the valve fromatmosphere preventing the escape of fuel from the valve.

The preferred embodiment of the valve packing assembly contained in thestuffing,box is shown in an exploded format in FIG. 2. To seal the valveshaft, a compression member 20 is placed over the valve shaft and slidover the shaft into the stuffing box. The compression member, preferablya coiled spring with an aperture sized to receive the valve shaft,engages an upper wall 22 (FIG. 1) of the stuffing box. A set of threepacking rings 24, 26, 28 is placed over the shaft and slid into thestuffing box up against the compression member. In the preferredembodiment shown, all three rings are generally V-shaped as shown inFIGS. 3 and 4; This V-shaped ring is commonly referred to as a chevronshaped ring. A cross-section of the V-shape is generally triangular witha central triangular opening 40 and a crown 38. The crown 38 of thepacking rings may be more rounded than is shown, or flat, and the wallthickness can be varied. In the preferred embodiment the packing ringsare made from graphite impregnated TEFLON®.

Referring back to FIG. 2, after the first set of three packing rings ispushed into the stuffing box, a conventional lantern ring 30 is placedover the shaft and pushed into the stuffing box. After the lantern ring,a second set of three packing rings 32, 34, 36 is placed over the shaftand pushed into the stuffing box. The crown 38 of the packing rings 28,32 closest to the lantern ring are preferably oriented toward thelantern ring. The V-shape of the packing rings 28, 32 next to thelantern ring may be modified to have a flat crown, but if modified, itstill includes the triangular opening 40.

The contents of the stuffing box are held in place by a packing gland 42shown in detail in FIGS. 5 and 6. The packing gland is attached to thevalve where the valve shaft enters the stuffing box. The packing glandhas a central aperture 45 sized to receive the valve shaft, and thepacking gland has a flange 44 which extends into the stuffing box. Thepacking gland has four apertures 46 through which bolts are inserted toattach the packing gland to the valve. Further, the central aperture ofthe packing gland has a counterbore 48 to receive a sealing ring 50.During operation, portions of the valve shaft are translated in and outof the stuffing box. The sealing ring, which is preferablyspring-loaded, seals against the valve shaft and the packing gland toprevent foreign matter from entering the stuffing box and damaging thevalve packing. Thus, as the valve shaft is translated in a directionwhich brings externally exposed portions of the valve shaft into thestuffing box, any foreign matter on the valve shaft contacts the sealingring, and the sealing ring prevents the foreign matter from entering thestuffing box.

When the packing gland is tightened onto the valve, the compressionmember is compressed, thereby compressing the V-shaped packing rings sothat the crown of the packing rings is pushed toward the center of thepacking rings and into the opening 40. The compression force expands thepacking rings radially outward and inward to sealably engage the valveshaft and the vertical wall 52 of the stuffing box. Compression morereadily expands the V-shaped packing rings, than packing rings withother shapes because the crown is readily forced into the triangularopening thereby forcing the outer edge 41 outwardly against the stuffingbox wall and the inner edge 43 inwardly against the valve shaft. Becausethe V-shaped rings seal more efficiently and because there are two setsof packing rings, the frequency of leaks is reduced, thereby reducingthe member of environmentally required valve packing repairs andeliminating environmental compliance problems.

The valve shaft 16 extends through the packing in the stuffing box outof the central aperture of the packing gland and extends up to acrosshead 54. The crosshead terminates at a body 56 which is split intotwo legs 58, 60. The two legs define a generally cylindrical shaftreceiving area 58 therebetween. The valve shaft extends into a valveshaft receiving side of the crosshead approximately half way through theshaft receiving area to a point where a bore 60 through the valve shaftis aligned with a bore 62 through the body of the crosshead. A threadedvalve shaft pin 64 extends through the bores 60, 62 and is engaged by anut 66 which is tightened onto the valve shaft pin and held tight with alock washer 68 or other mechanism such as a cotter pin to hold the valveshaft in place in the shaft receiving area. A stub shaft 70, which ismuch shorter than the valve shaft, is engaged by the actuator andextends into the body of the crosshead. When the stub shaft is insertedapproximately half way into the stub shaft receiving side of thecrosshead body, a bore 72 in the stub shaft is aligned with a bore 74 inthe body of the crosshead. A threaded stub shaft pin 76 is insertedthrough the bores 72, 74 and secured therein by a nut 78 and lock washer80 or other mechanism. Thus, the bifurcated shaft parts are held in anabutting relationship.

Once the valve shaft and stub shaft are held in place by the pins 64,76, a tightening mechanism generally designated 82 is used to pinch thetwo legs of the crosshead together, thereby tightly securing the stubshaft and valve shaft in the shaft receiving area. The preferredembodiment of the tightening mechanism is simply a large threaded pin 82which is inserted through bores 84 in the legs of the body and tightenedwith a nut 86. The nut is held tight with a lock washer or othermechanism preventing rotation of the nut relative to the pin such as acotter pin.

The distance X between the bottom of the cabinet and the bottom of thevalve is approximately 10 inches. Because of this small amount ofavailable work space in the cabinet, it was previously necessary todismantle the entire valve to repair and change the valve packingassembly. With the present invention, it is not necessary to disassemblethe valves to repair the valve packing assembly. In a preferredembodiment of the present invention, the tightening mechanism isloosened, the stub shaft pin 76 is removed, and the stub shaft isremoved from the assembly. Then the valve shaft pin is removed and thecrosshead can be removed from the cabinet. Next, the packing gland isdetached from the valve to open the stuffing box. The packing gland isslid off of the shaft and the sealing ring can be scraped out of thecounterbore in the packing gland while the packing gland is at a workstation. This is quicker and easier than scraping the sealing ring offthe hard to reach stuffing box wall in the valve as previously required.The valve shaft can then be slid longitudinally in a direction out ofthe valve, so that the valve shaft is partially out of the valve adistance at least equal to the length of the stub shaft, thereby pullingall of the stuffing box contents out of the stuffing box. Therefore, theold valve packing is easily pulled off of the shaft; the shaft iscleaned; the replacement packing is placed back on the valve shaft andpushed back into the stuffing box; the packing gland is attached to thevalve; the crosshead body is reattached to the valve shaft, and the stubshaft is reattached to the crosshead body. By removing the stub shaft,the limited work space in the cabinet is sufficient to allow the valvepacking assembly to be changed without dismantling the valve. Utilizingthis invention, packing changes are completed in approximately four (4)hours.

Thus, a valve packing replacement method and valve packing are disclosedwhich utilize V-shaped TEFLON® packing rings which are graphiteimpregnated to more efficiently seal the turbine fuel valve and abifurcated shaft to more efficiently effect valve packing changes. Whileembodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art that manymore modifications are possible without departing from the inventiveconcepts herein. It is, therefore, to be understood that the scope ofthe invention should be directed only by the appended claims, wherein

What is claimed is:
 1. A valve packing assembly for sealing a shaft of avalve to prevent leaks, the shaft extending through a stuffing box andhaving an end external to the valve, the valve packing assemblycomprising:a) a compression member on the valve shaft and against thestuffing box; b) at least one compressible first packing ring on thevalve shaft and against the compression member; c) at least onecompressible second packing ring on the valve shaft; d) a lantern ringon the valve shaft between the first packing ring and the second packingring; g) a stub shaft; and h) a joint detachably connecting the stubshaft and the end of valve shaft external to the valve.
 2. The valvepacking assembly of claim 1, wherein the stub shaft and the valve shaftare in abutting relative contact.
 3. The valve packing assembly of claim1, further comprising a packing gland disposed on the valve shaft andagainst the second packing ring, the packing gland being attachable tothe valve at a location at which the valve shaft enters the stuffingbox.
 4. A valve packing assembly for sealing a shaft of a valve toprevent leaks, the shaft extending through a stuffing box, the valvepacking assembly comprising:a) a compression member on the valve shaftand against the stuffing box; b) at least one first packing ring on thevalve shaft and against the compression member; c) a lantern ring on thevalve shaft and against the first packing ring; d) at least one secondpacking ring on the valve shaft and against the lantern ring; e) apacking gland on the valve shaft and against the second packing ring,the packing gland being attachable to the valve at a location at whichthe valve shaft enters the stuffing box; and f) a stub shaft detachablyconnected to the valve shaft external to the valve.
 5. The valve packingassembly of claim 4, comprising a plurality of first packing rings onthe valve shaft and against the compression member, and a plurality ofsecond packing rings on the valve shaft and against the lantern ring. 6.The valve packing assembly of claim 5, wherein at least one of each ofthe first and second packing rings comprises a V-shaped, graphiteimpregnated ring.
 7. The valve packing assembly of claim 4, wherein thepacking gland has a counterbore, and further comprising a sealing ringin the counterbore and on the valve shaft.
 8. The valve packing assemblyof claim 4, further comprising a crosshead detachably connecting thestub shaft and the valve shaft.
 9. The valve packing assembly of claim8, wherein the crosshead defines a first bore sized to receive the valveshaft, and a second bore sized to receive the stub shaft, the first borebeing aligned with the second bore.
 10. The valve packing assembly ofclaim 9, further comprising a first fastener removably retaining thevalve shaft in the first bore, and a second fastener removably retainingthe stub shaft in the second bore.
 11. A valve packing assembly forsealing a valve shaft of a turbine fuel valve to prevent leaks, theturbine fuel valve having a wall defining a chamber, the valve shaftextending through a stuffing box in the chamber and external to thechamber, the valve packing assembly comprising:a) a compression memberon the valve shaft and against the stuffing box; b) at least one firstpacking ring on the valve shaft and against the compression member; c)an intermediate ring on the valve shaft and against the first packingring; d) at least one second packing ring on the valve shaft and againstthe intermediate ring; e) a packing gland on the valve shaft and againstthe second packing ring; f) at least one fastener for removablyattaching the packing gland to the wall of the valve; g) a stub shaft;and h) a connector for selectively joining the valve shaft and the stubshaft external to the chamber.
 12. The valve packing assembly of claim11, wherein the connector comprises a crosshead having a pair of alignedbores sized to receive the valve shaft and the stub shaft in abuttingrelationship.
 13. The valve packing assembly of claim 11, wherein theintermediate ring is a lantern ring, and comprising a plurality of eachof the first and second packing rings.
 14. The valve packing assembly ofclaim 11, wherein the packing gland has a counterbore, and furthercomprising a sealing ring in the counterbore and on the valve shaft. 15.The valve packing assembly of claim 11, wherein the stub shaft has alength such that when the stub shaft and the connector are disconnectedfrom the valve shaft, the stuffing box is removable from the chamber ofthe valve.
 16. A valve packing assembly for sealing a valve shaftdisposed in a cabinet, the valve having a wall spaced from the cabinetand defining a chamber, the valve shaft extending through a stuffing boxin the chamber, the valve shaft the valve packing assembly comprising:a)a compression member on the valve shaft and against the stuffing box; b)at least one first packing ring on the valve shaft and against thecompression member; c) an intermediate ring on the valve shaft andagainst the first packing ring; d) at least one second packing ring onthe valve shaft and against the intermediate ring; e) a packing gland onthe valve shaft and against the second packing ring; and f) a stub shaftselectively attachable to the valve shaft, the stub shaft having alength such that when the stub shaft is detached from the valve shaft,the valve shaft can be translated toward the cabinet a distance equal toat least the length of the stub shaft to enable the compression member,the first packing ring, the intermediate ring and the second packingring to be removed from the chamber and positioned between the wall andthe cabinet.
 17. The valve packing assembly of claim 16, furthercomprising a sealing ring on the valve shaft against the packing gland,the sealing ring seals the valve shaft and packing gland to preventforeign matter from entering the stuffing box from outside the stuffingbox.
 18. The valve packing assembly of claim 16, wherein theintermediate ring is a lantern ring, and comprising a plurality of eachof the first and second packing rings.
 19. The valve packing assembly ofclaim 16, wherein the wall is spaced a distance of approximately 10inches from the cabinet.